Suspension spring system

ABSTRACT

A suspension spring system includes a housing, a suspension spring located in the housing and a bistable control spring located in the housing. A load supporting member is positioned at least partially within the housing and is movable with respect to the housing. The control spring is radially compressed within the housing so that the control spring is prestressed. The control spring is shiftable between two stable final positions and is, thus, able to influence and control the spring characteristics of the suspension spring.

BACKGROUND OF THE INVENTION

The present invention relates to a suspension spring system.

Especially, the invention relates to a spring system with a softsuspension spring, whereat said soft suspension spring is a tensionspring or a pressure spring.

Soft suspension springs with a flat linear force-deflection curve aretheoretically perfect for supporting and suspension purposes in numerousapplications. Practically, however, their use almost always failsbecause the spring strokes are too large, because the material of thesoft suspension spring, which may be spring steel or elastomer material,the high local loads connected therewith, and because the hard action ofthe necessary end stop means limit the spring stroke.

Similar problems arise when using stiffer and mechanically more rigidsuspension springs that undergo large, especially dynamic loads.

Thus, the invention is designed to provide a suspension spring systemwhich, particularly when using a soft and/or highly loaded suspensionspring, shows a high mechanical stability under load and a long workinglife even when undergoing dynamic loads. Additionally, when leaving thelinear working range, the limitation of the spring stroke is to startsoftly without any hard stop characteristics without having to use softstop buffers which would have to undergo too high requirements withrespect to their mechanical stability.

OBJECTS AND SUMMARY OF THE INVENTION

For solving this problem, a suspension spring system according to thepresent invention includes a bistable control spring coupled to asuspension spring, wherein both stable final positions of said controlspring are on top of each other with respect to the direction of thespring deflection path of the suspension spring.

The suspension spring system according to the present inventioncomprises two essential and fundamental advantages: (1) The controlspring may have a high or very high mechanical rigidity, so that thecontrol spring is able to protect effectively a soft suspension springwithout changing significantly by the unstable range of itsforce-deflection curve the force-deflection curve of the suspensionspring within the coupled range. (2) The control spring used in asuspension spring system according to the present invention shows aforce-deflection curve starting from a first overstretched final range,followed by a first stable final range, then changing from an unstableintermediate range showing practically almost a zero spring ratefollowed by the range of the restoring force of the control spring to asecond stable final range, followed again by a second overstretchedfinal range. In a suspension spring system according to the presentinvention, this force-deflection curve of said control spring is actingadditively to the force-deflection curve of the suspension spring, sothat a person skilled in the art constructing a suspension spring systemaccording to the principles of the present invention has practicallyunlimited possibilities for influencing the force-deflection curve ofthe suspension spring system by choosing the working range of the springcharacteristics of the control spring according to the respectiveapplication.

Preferably, the control spring is used such that the unstable neutralrange of the control spring with respect to the spring deflection path,which is in-between the two stable final positions of the controlspring, is within the working range of the suspension spring, which inmost applications will be linear. For realizing such a suspension springsystem, a person skilled in the art will find a large number of possiblespring combinations without any problems. Preferably, the suspensionspring system is formed such that the suspension spring is a pressurespring or a tension spring and the control spring is either a pressureor a tension spring radially pre-stressed with respect to the suspensionspring, or a pressure or tension spring system consisting of severalpressure or tension springs with or without inserted lever systems, or adisc spring, or a bistable leaf spring.

Especially, when the suspension spring system is used as an axialbearing or a suspension bearing, the suspension spring is preferably arubber buffer, the load supporting member of which is coupled centrallyto a rubber disc or a rubber disc spring pre-stressed radiallycompressively with respect to a stationary load transferring member.

Particularly, when the rubber buffer serving as a suspension springconsists of an extraordinarily soft elastomer material or a rubberspring with cavities inside, an extremely soft, but, at the same time,extremely stable and mechanically rigid bearing is achieved by using acontrol spring pre-stressed according to the requirements. Such abearing changes gradually softly and without any end stopcharacteristics from the linear working range of the suspension springto a limiting progressive range, if the elasticity of the control springis dimensioned accordingly.

However, the control spring is not only able to influence and controlthe spring characteristics and the force-deflection curve of thesuspension spring undergoing an axial load, but it can also simplycompensate asymmetric radial loads by a corresponding asymmetricconstruction. For realizing the compensation of radial loads, a personskilled in the art will once again easily find many possibilities. Whenusing a compressively pre-stressed disc-type rubber control spring, adifferentiated compensation is particularly simple in that the disc-typerubber control spring includes axially extending cavities, recesses,channels or openings. These cavities weaken the restoring force of thedisc-type rubber control spring with respect to a radial directionaccording to the distribution of the cavities, wherein these cavities,recesses, channels or openings may be open at both sides, which meansthat they pass through the spring, or closed at one side. Additionally,an asymmetric distribution of the radial spring forces of the controlspring can be easily achieved by a differentiated thickness of thedisc-type rubber control spring.

For special applications, when a soft suspension spring and a controlspring, which is not very stiff, are required at the same time torealize a certain predetermined spring characteristic curve of asuspension spring system, the axial spring stroke of the control spring,axial with respect to the suspension spring, can be limited by end stopmeans, too. Since such end stop means that limit the spring stroke ofthe control spring are only acting indirectly and partially upon theforce-deflection curve of the whole suspension spring system, such endstop means are not critical for most applications. When using disc-typecontrol springs, the end stop means for limiting the spring stroke ofthe control spring are preferably formed as disc-type means which areattached rigidly or elastically to the load supporting member above andbelow the control spring and at least essentially parallel to thecontrol spring.

Preferably, such end stop means for limiting the spring stroke of thecontrol spring are provided when, according to a further embodiment ofthe invention, the control spring is an annular disc-type spring made ofan elastomer material, which is radially pre-stressed and which enclosesthe soft suspension spring of the spring system peripherally. Inaddition to that control spring, a suspension spring is preferablyarranged within a two-part housing. The two housing parts arebeaker-type or bell-type and overlap each other axially allowing acertain radial free motion such that the control spring is fixed andradially pre-stressed between the overlapping surface areas of the twohousing parts. In this embodiment of a suspension spring system, the endstop means limiting the spring stroke of the control spring arepreferably formed directly from and are parts of the surface areas ofthe housing parts.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is described more in etail with anembodiment of the invention together with the accompanying drawings, andwherein

FIG. 1 is a longitudinal cross-sectional view of an embodiment of asuspension spring system according to the invention, wherein the portionon the left of the central axis is statically loaded and the portion onthe right of the central axis is unloaded;

FIG. 2 is the force-deflection curve of the spring characteristics of acontrol spring as shown in FIG. 1;

FIG. 3 is the force-deflection curve of a soft rubber suspension springas shown in FIG. 1;

FIG. 4 is the force-deflection curve of a suspension spring system asshown in FIG. 1, achieved by addition of a force-deflection curve of acontrol spring according to FIG. 2 and a force-deflection curve of asuspension spring according to FIG. 3; and

FIG. 5 is a longitudinal cross-sectional view of a further embodiment ofa suspension spring system, wherein the cutting planes of the left partand the right part of this figure are rotated 90° with respect to eachother along the central axis of the suspension spring system.

FIG. 6 is a longitudinal cross-sectional view similar to FIG. 1 of afurther embodiment of a suspension spring system according to thepresent invention showing the control spring in the form of a rubberdisc having axially extending channels therein;

FIG. 7 is a longitudinal cross-sectional view similar to FIG. 1 ofanother embodiment of a suspension spring system according to thepresent invention showing the control spring in the form of a rubberdisc having axially extending cavities therein; and

FIG. 8 is a slightly enlarged cross-sectional view along the line 8--8of FIG. 7 showing the plurality of pressure springs that define apressure spring system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The suspension spring system shown schematically in FIG. 1 consistsessentially of a suspension spring 1 and a control spring 2. Thesuspension spring 1 is a cylindrically shaped rubber buffer withcavities inside, which is arranged in a beaker-type housing 3, thebottom 4 of which serves as a load transferring member to the suspensionspring 1. The housing 3 may comprise for example an outer flange 5 withbores 6, by which the housing 3 can be attached rigidly to a referencesystem, for example an engine frame.

The control spring 2 is a disc-type rubber member which is at leastessentially symmetrical with respect to its horizontal main plane. Thecontrol spring 2 is formed thicker around a central sleeve 7 serving asa load supporting member of the suspension spring system than at itsouter edges.

At both ends of the sleeve 7, disc-type members 8,9 having a certainprofile are fixed, which serve as end stop for means limiting the springstroke of the control spring 2.

The control spring 2 is pre-fabricated separately. Not pre-stressed, thecontrol spring comprises an outer diameter, which is larger than theinner diameter of the housing 3 at that place, where the control spring2 is inserted as can be seen from FIG. 1. This means, that the controlspring 2 is radially compressively pre-stressed when it is inserted intothe upper rim of the housing 3. If there is no obstruction, the controlspring 2 tries to evade that deformation by curving axially concavely orconvexly, whereat both ways of curving result in a certain minimum ofremaining stress which is the same in both directions. Thus, the controlspring 2, which is radially pre-stressed as can be seen from FIG. 1,comprises two stable final positions which are equivalent with respectto its energy, which means it is "bistable". When converting the controlspring 2 from its one final position to its other, which happens, forexample, when the convex final position is "pressed" to the concavefinal position, an unstable intermediate range will be passed, whichrange is characterized in its center by a symmetric distribution of thedeformation stress at both sides of the main plane of the stress-loadedcontrol spring 2. In this range, the axial spring rate of the controlspring 2 is practically about zero. Not until this unstable range, whichcorresponds to the range of the maximum deformation of the spring, hasbeen passed, a spontaneous restoration of the control spring 2 into thesecond final position, which is in this embodiment the concavely curvedfinal position, takes place. The specific course of the force-deflectioncurve of the control spring 2 depends primarily from the compressivestress acting upon the control spring 2 and secondarily from the profileof the control spring 2. Typical spring characteristics of such controlsprings are shown schematically in FIG. 2. In that illustration, themore or less negatively extending sections of the force-deflection curvecorrespond to the spontaneous restoring or "turning-over" of thepre-stressed control spring 2 into the second stable final position, andthe progressive rising sections of the curve in the right part of FIG. 2correspond to the concave overstretching of the control spring.

In the illustration of FIG. 1, right from the center line 10, thecontrol spring 2 is shown in its convex stable final position when thesuspension spring system is unloaded. Left from the center line 10, thecontrol spring 2 is shown in its unstable neutral position when thesuspension spring system is loaded.

As can be seen from FIG. 1, the suspension spring itself is acylindrical rubber block comprising cavities, which rubber block isdimensioned such that it sits close directly or indirectly, which meansseparated by a disc-type member 9, to the control spring 2 beingunstressed in its upper final position. In this arrangement, thesuspension spring 1 is not pre-stressed or only minimally axiallypre-stressed. It can be seen easily by a person skilled in the art, thatthe pre-stress of the springs 1 and 2 can be predetermined easily withinany range according to the requirements of the specific applications.

Without comprising any control spring, the rubber block with cavitiesinside serving as a suspension spring 1 shows the force-deflection curveas can be seen from FIG. 3, wherein the working range is used for thesuspension spring system of FIG. 1. In FIG. 3 as well as in FIGS. 2 and4, the reference letter F means spring force and the reference letter smeans spring stroke.

When assembling and coupling the suspension spring 1 and the controlspring 2, as can be seen from FIG. 1, the characteristicforce-deflection curve of the suspension spring 1 and of the controlspring 2 are added to result in a characteristic curve of the suspensionspring system. The typical course of such a characteristic curve of asuspension spring system according to FIG. 1 is shown graphically inFIG. 4. That force-deflection curve is characterized by an extremelysoft, which means flat linear working range, which, if required, can beformed even softer than the suspension spring 1 can provide by itself,and which changes gradually and softly to the following progressiverange. However, of much more importance than the soft changing into theprogressive range is the effect, that the extremely soft linearcharacteristic curve can be used permanently by relatively high loads,because a much more rigid and resistant elastomer material can be usedthan it is possible when realizing a force-deflection curve according toFIG. 3 for the suspension spring 1 by itself.

Assuming that the suspension spring system shown in FIG. 1 right fromthe center line 10 corresponds to the unloaded state of the suspensionspring system as described above. Further assuming that when having astatic load, the suspension spring system converts to the state shown inFIG. 1, left from the center line 10. This would correspond to a staticoperating point, which is about in the center range of the linearsection of the force-deflection curve of the suspension spring systemshown in FIG. 4. Vibrations of that load acting relative to the loadtransferring member 4 in both axial directions can be cushionedextraordinarily softly by the suspension spring system described above,wherein the suspension spring 1 itself is only minimally mechanicallyloaded.

It can be seen easily from the specification above, that, for example,by changing the dimensions, the material characteristics of the springs1,2 and/or the pre-stress which has to be adapted to the specificrequirements, the operating point can be shifted from the center of thelinear section of the characteristic curve shown in FIG. 4 to the leftor right edge or beyond. Where such operating points have to placeddepends only from the specific requirements of the application and caneasily be determined by a person skilled in the art in standard tests.

In FIG. 5 there is shown a further embodiment of a suspension springsystem. In the longitudinal section of FIG. 5, the cutting plane leftfrom the center line 10 and right of the center line 10 are rotated by90° around the center line with respect to each other such that when oneof the two cutting planes is within the drawing plane, the other cuttingplane is perpendicular with respect to the drawing plane and intersectsthe drawing plane along the center line.

The housing of the suspension spring system consists of two beaker-typeor bell-type housing parts being open axially towards each other andoverlapping each other telescopically. In the following, these housingparts are called "load supporting housing parts" 11 and "loadtransferring housing part" 12.

In the illustration of FIG. 5, the suspension spring system is shownundergoing a certain static load neither shown nor referenced in FIG. 5.This means, that the illustration shown in FIG. 5 corresponds to theillustration shown in FIG. 1, left from the center line 10.

An annular disc-type control spring 2' is fixed under a radialcompressive force between the sections of the housing 11,12 overlappingeach other and is thus allowed a certain radial free motion. End stopmeans limiting the spring stroke 13,14, respectively 15, 16, forlimiting the positive (13,14) and negative (15,16) deflection range ofthe control spring are formed uniformly angularly spaced andalternatingly at the two housing parts overlapping each other. The endstop means 13,14,15,16 are formed by inclined surface areas, which areparallel and complementary with respect to each other and which surfaceareas are dimensioned such that, on the one hand, they avoid anexcessive curvature of the annular disc-type control spring pre-stressedin an unstable position, and, on the other hand, they do not effect asudden and hard limiting of the spring stroke of the control spring, buta gradually progressive rising of the characteristic curve, wherein thecontrol spring is undergoing a tensile load.

The embodiment of the suspension spring system shown in FIG. 5 is aparticularly robust and compact bearing for motor suspension, which isnearly closed in itself. The bearing comprises a threaded bolt 17 fortightening the load, which means here the engine, and the threaded bolt18 for connecting the bearing to the frame part supporting the motorblock or the engine.

The construction of the suspension spring and the possibilities ofadjusting the characteristics of the bearing correspond to thecharacteristic features described above with respect to the illustrationof FIG. 1.

As mentioned earlier, the bistable control spring can be adapted to notonly control and influence the spring characteristics of the suspensionspring in response to axial loads but in addition, to compensateasymmetric radial loads. In order to achieve that latter objective, thecontrol spring 2 can be manufactured in the form of a rubber disc havinga plurality of axially extending channels 19 located therein as seen inFIG. 6. Alternatively, the control spring 2 could be manufactured in theform of a rubber disc having a plurality of axially extending cavities20 located therein in a manner such as that illustrated in FIG. 7.

As shown in FIG. 8 and as mentioned previously, the bistable controlspring can also be manufactured as a pressure spring system comprised ofa plurality of pressure springs 2.

While the invention has been described and illustrated in accordancewith preferred embodiments, it is recognized that variations and changesmay be made and equivalents employed herein without departing from theinvention as set forth in the claims.

We claim:
 1. A suspension spring system comprising:a housing; a loadsupporting member at least partially positioned within said housing andmovable with respect to said housing; a suspension spring located insaid housing, said suspension spring comprising a soft rubber springhaving a plurality of cavities located therein, said suspension springbeing compressible in an axial direction; a disc-shaped bistable controlspring means located in said housing for influencing and controlling thespring characteristics of said suspension spring, said disc-shapedbistable control spring means comprising at least one pressure spring,said disc-shaped bistable control spring means being mounted on saidload supporting member and being radially compressed within said housingso as to be prestressed, said disc-shaped bistable control spring meansbeing shiftable between two different final positions in response tomovement of said load supporting member, both of said final positionsbeing stable and being located along the axis of compression of saidsuspension spring.
 2. A suspension spring system in accordance withclaim 1, wherein said disc-shaped bistable control spring meanscomprises a rubber disc having axially extending cavities therein.
 3. Asuspension spring system in accordance with claim 1, wherein saiddisc-shaped bistable control spring means comprises a rubber disc havingaxially extending passing channels therein.
 4. A suspension springsystem in accordance with claim 1, wherein said disc-shaped bistablecontrol spring means comprises several pressure springs that define apressure spring system.
 5. A suspension spring system in accordance withclaim 1, wherein said disc-shaped bistable control spring means movesthrough an intermediate range as the disc-shaped bistable control springmeans shifts from one of said final stable positions to the other ofsaid final stable positions, said disc-shaped bistable control springmeans being unstable in the intermediate range.
 6. A suspension springsystem comprising:a housing; a load supporting member at least partiallypositioned within said housing and movable with respect to said housing;a suspension spring located in said housing, said suspension springcomprising a soft rubber spring having a plurality of cavities locatedtherein, said suspension spring being compressible in an axialdirection; and a disc-shaped bistable control spring means located insaid housing for influencing and controlling the spring characteristicsof said suspension spring, said disc-shaped bistable control springmeans comprising at least one pressure spring, said disc-shaped bistablecontrol spring means being mounted on said load supporting member andbeing radially compressed within said housing so as to be prestressed,said disc-shaped bistable control spring means being shiftable betweentwo different final positions in response to movement of said loadsupporting member, both of said final positions being stable and beinglocated along the axis of compression of said suspension spring; and atleast one end stop means associated with said disc-shaped bistablecontrol spring means for limiting an effective spring stroke of saiddisc-shaped bistable control spring means.
 7. A suspension spring systemin accordance with claim 6, comprising two end stop means, each end stopmeans being attached to said load supporting member and said disc-shapedbistable control spring means being positioned between said two end stopmeans.
 8. A suspension spring system in accordance with claim 7, whereineach of said end stop means comprises a disc.
 9. A suspension springsystem in accordance with claim 6, wherein one end of said suspensionspring is positioned against a load transferring member of said housingwhich is defined by a bottom portion of said housing and an opposite endof said suspension spring contacts said end stop means.
 10. A suspensionspring system in accordance with claim 6, wherein said disc-shapedbistable control spring means moves through an intermediate range as thedisc-shaped bistable control spring means shifts from one of said finalstable positions to the other of said final stable positions, saiddisc-shaped bistable control spring means being unstable in theintermediate range.
 11. A suspension spring system comprising:a housing;a load supporting member at least partially positioned within saidhousing and movable with respect to said housing; a suspension springlocated in said housing, said suspension spring comprising a soft rubberspring having a plurality of cavities located therein, said suspensionspring being compressible in an axial direction; and disc-shapedbistable control spring means located in said housing for influencingand controlling the spring characteristics of said suspension spring,said disc-shaped bistable control spring means comprising at least onepressure spring, said disc-shaped bistable control spring means beingradially compressed within said housing so as to be pre-stressed, saiddisc-shaped bistable control spring means being shiftable between twodifferent final positions in response to movement of said loadsupporting member, both of said final positions being stable and beinglocated along the axis of compression of said suspension spring; and atleast one end stop means associated with said disc-shaped bistablecontrol spring means for limiting an effective spring stroke of saiddisc-shaped bistable control spring means, said end stop meanscomprising a disc attached to said load supporting member and extendingin a direction transverse to the direction of compression of saidsuspension spring.
 12. A suspension spring system in accordance withclaim 11, comprising two end stop means attached to said load supportingmember, said disc-shaped bistable control spring means being positionedbetween said two end stop means.
 13. A suspension spring system inaccordance with claim 11, wherein said disc-shaped bistable controlspring means moves through an intermediate range as the disc-shapedbistable control spring means shifts from one of said final stablepositions to the other of said final stable positions, said disc-shapedbistable control spring means being unstable in the intermediate range.14. A suspension spring system comprising:a housing formed by twohousing parts, one of said housing parts being axially and telescopinglypositioned within the other housing part so that the one housing part isradially movable with respect to the other housing part, portions of theone housing part overlapping portions of the other housing part; asuspension spring located in one of said housing parts; and an annular,disc-shaped bistable control spring means positioned between theportions of the housing parts which overlap each other for influencingand controlling the spring characteristics of the suspension spring,said disc-shaped bistable control spring means being radially compressedbetween said overlapping portions so as to be pre-stressed, saiddisc-shaped bistable control spring means being shiftable between twodifferent final positions in response to movement of said housing partsrelative to one another, both of said final positions being stable andbeing located along the axis of compression of said suspension spring,said housing parts including end stop means for limiting an effectivespring stroke of said disc-shaped bistable control spring means.
 15. Asuspension spring system in accordance with claim 14, wherein said endstop means comprises spaced, inclined surfaces located on portions ofsaid housing parts which overlap each other.
 16. A suspension springsystem in accordance with claim 15, wherein the spaced inclined surfacesof said one housing part extend over one side of said disc-shapedbistable control spring means at first locations and extend over anopposite side of said disc-shaped bistable control spring means atsecond locations, the inclined surfaces of said other housing partextend over said opposite side of said disc-shaped bistable controlspring means at said first locations and extend over said one side ofsaid disc-shaped bistable control spring means at said second locations.17. A suspension spring in accordance with claim 16, wherein theinclined surfaces of said one housing part and said other housing partat said first location are substantially parallel and wherein theinclined surfaces of said one housing part and said other housing partat said second locations are substantially parallel.
 18. A suspensionspring system in accordance with claim 14, wherein said disc-shapedbistable control spring means moves through an intermediate range as thedisc-shaped bistable control spring means shifts from one of said finalstable positions to the other of said final stable positions, saiddisc-shaped bistable control spring means being unstable in theintermediate range.
 19. A suspension spring system comprising:a housing;a load supporting member at least partially positioned within saidhousing and movable with respect to said housing; suspension springmeans located in said housing for elastically supporting said loadsupporting member, said suspension spring means being compressible in anaxial direction and comprising a soft rubber spring having a pluralityof cavities therein; and disc-shaped bistable control spring meanslocated in said housing for influencing and controlling the springcharacteristics of the suspension spring means, said disc-shapedbistable control spring means being mounted on said load supportingmember and being radially compressed within said housing so as to bepre-stressed, said disc-shaped bistable control spring means beingshiftable from a first final position, through an intermediate range andto a second final position in response to movement of said loadsupporting member, said first and second final positions of saiddisc-shaped bistable control spring means being stable and being locatedalong the axis of compression of said suspension spring means, saidintermediate range of said disc-shaped bistable control spring meansbeing unstable.
 20. A suspension spring system in accordance with claim19, wherein said disc-shaped bistable control spring means has asubstantially zero spring rate when the disc-shaped bistable controlspring means is in the intermediate range.
 21. A suspension springsystem in accordance with claim 19, wherein said suspension spring meansis an elastomeric member and said disc-shaped bistable control springmeans is a rubber member.
 22. A suspension spring system in accordancewith claim 19, wherein when said disc-shaped bistable control springmeans is in its first final position, said disc-shaped bistable controlspring means is concave and when said disc-shaped bistable controlspring means is in its second final position, said disc-shaped bistablecontrol spring means is convex.
 23. A suspension spring system inaccordance with claim 6, wherein said disc-shaped bistable controlspring means comprises several pressure springs that define a pressurespring system.
 24. A suspension spring system in accordance with claim11, wherein said disc-shaped bistable control spring means comprisesseveral pressure springs that define a pressure spring system.
 25. Asuspension spring system in accordance with claim 19, wherein saiddisc-shaped bistable control spring means moves through an intermediaterange as the disc-shaped bistable control spring means shifts from oneof said final stable positions to the other of said final stablepositions, said disc-shaped bistable control spring means being unstablein the intermediate range.